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Andrew Robertson

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  1. Hi efi265, I had a similar problem with idle hanging high, also using a GM style idle stepper motor that was part of a holley 1000cfm throttle body MPEFI chev 383 set-up using closed loop idle control. It was a few years ago but from memory, here is how I licked it: 1. Firstly you have to identify the stepper values that equate to the IAC valve being fully closed. Do this by switching to open loop and physically looking at the IAC valve head while it is installed in the throttle body (car not running) and keep raising the stepper value in the table until the IAC no longer visibly moves any further closed. Then back off 1 point, then set that as your max clamp value. That means the IAC will never be instructed by the ECU to go beyond fully closed and will therefore never get out of kilter with the ECU. To get a decent min clamp value, still in open loop, with a warm engine set the IAC far enough open to give you around 2500 rpm and note that value - set min clamp at that value. Set TP Lockout to around 1% and RPM lockout to around 300-400. 2. Still in open loop, with the engine warm, set the stepper motor value to the max clamp level so the IAC is closed, and adjust the throttle stop so that the engine is idling about 100-150 rpm below your target idle speed. Then do a TPS calibration and ensure that the TP position goes to 0% when the throttle is fully closed. 3. Still in open loop, with the engine completely cold, fire it up from cold and adjust the stepper motor values in the table for each temperature cell so that under 60C engine temp, you are idling around 150-200 RPM slower than your target closed loop idle speed for that temp, and above 60C you are idling around 100 rpm slower than your target RPM closed loop idle speed for that temp. Basically create a set of open loop stepper motor values that have the car idling quite a bit slower than desired at all temperatures. The IAC should be very near the max clamp value with the engine at operating temp. This set-up process is important and it's the key to success. 4. Switch back to closed loop and fine tune tune from there. If it still hangs high, try increasing stepper motor value slightly, or increasing RPM lock-out slightly, or both. If it drops under target and then recovers or starts to hunt, drop stepper motor value slightly. The reason the set-up approach in 3 is important is that when you set control to closed loop, when the throttle goes under 1% and RPM falls under the RPM lockout value (like when you coast to the lights), the ECU implements a ramping strategy that you have no control over. To smoothly drop RPM down to target the ECU subtracts a fixed non-user-adjustable number of steps off the stepper motor table value for about a second, and then adopts the table value for about a second, and then adopts closed loop control. If you have a stepper motor table value too low to start with, at the first stage of this ramping strategy the rpm will hold or rise outside the rpm lockout point again and the car will hang above this point or hunt around it. The reason my car was prone to this is that the GM stepper motor flows shitloads of air and the non-user-adjustable number of steps that the ECU took off the table value at the first stage of this ramp back to closed loop actually increased my idle speed rather than gently guiding it down. The bandaid approach was basically to have stepper motor values in the table that caused the IAC to be more closed during the non-controllable part of the ramping strategy than it otherwise would be. Idling when warm in closed loop my stepper values would generally be 5-8 steps higher than the base value in the table. Let me know how you go. My Chev was boosted too - I don't think your issue will be boost related. Hope this helps. Inserted a screen shot of my idle set-up, done using this approach. Your stepper values won't be the same, but you get the idea. Cheers, Andrew Wellington NZ idle.doc
  2. Hi, Have a hilborn injected 434 Chev in a canam replica race car project controlled by G4 extreme running sequential. Engine has been dyno'd in the US - I know how much fuel it needs at WOT in each RPM increment for best power. I have it running well and have tuned idle and no load.  To get me in the ball park at WOT before I start testing can you pse supply fuel table values that will give approx the following injector duty cycles with a master fuel of 13: 16.8, 23.1, 29.9, 37.1, 47.2, 56.9, 64.7, 69.6, 72.2, 73.3. Not after any of your proprietory maths! - I would really appreciate your help. Email me offline at adr@xtra.co.nz if you prefer. Cheers, Andrew Robertson, Wellington
  3. Hi, got a 383 SB Chev turbocharged pump gas application running fairly high static compression and 5 speed manual trans, running G4 extreme sequential firmware 4.6.9.   I have ignition angle on boost set so the car can take boost without detonation in high gears like 4th and 5th where it sits there heavily loaded with RPM climbing relatively slowly. In second and third it can tolerate 2-4 degrees more timing in modes where it sweeps quickly up in RPM, and it feels noticably punchier in the mid range peak torque area if I dial in that extra timing, however this amount of timing causes det in taller gears on boost where RPM delta is lower. Is there an easy way to add an ignition trim to my on-boost timing based on RPM rate of change? I haven't got a knock sensor and don't really want to muck around with the installation of one, and I've got no easy way of telling the G4 what gear I'm in either. Cheers, Andrew
  4. Hi All, running sequential on old-school SB Chev with 1 ignition drive firing an MSD box / single coil / distributor, G4 Extreme firmware 4.6.9.  Trig 1 is a MSD flying magnet crank trigger that gives 4 pulses per rev, trig 2 is an optical shutter wheel arrangement inside the distributor that gives 1 pulse per 720 crank degrees.  This set-up has been running strong for about 3 years.  Problem now is an intermittent miss that has been showing up increasingly under higher loads and RPM - sometimes feels like a very short complete engine cut.  When this happens, I get a burst of trig 1 errors - the count will jump about 4-8 at a time. So a few questions: 1.  I assume that a problem downstream of the ignition drive (i.e. a problem with the MSD box, coil, cap/rotor, plug leads, or plugs) would NOT show up as a trig error, so I can safely assume the problem relates to triggering? 2.  What does a trig 1 error actually mean?  The crank trigger is trig 1 but these things are ultra-reliable - whereas trig 2 could well be the problem as I made that myself out of a gutted distributor and a modified unilite module.  Does trig 1 error basically mean there is a problem with the relationship between the two triggers seen by the ECU? 3.  When I first had the car running in a much earlier firmware version I used non-sequential batch mode, with 2 batches of 4 injectors, and simply used the crank trigger to drive it.  I have tried to go back to that now so I can determine whether trig 2 is the problem.  When I switch to multi-point batch mode I assumed trig 2 would disappear from the ignition menu and that I would simply have to enter a revised timing offset for trig 1 to get the car running?  The car will not start unless trig 2 stays configured as is.  How do I take it out of the equation to test it?  Why is it required in batch mode  - what am I doing wrong? Thanks, Andrew
  5. Hi All, might be missing something - can't work out how to take a PC log and save it as a comma delimited txt file so I can muck around with it in excel. My G4 xtreme was a very early version and came with the old-look PC link where export as a CSV was the only option. Now in the new look PC Link I can't work out how to save what I've logged as something usable outside PC Link.  Thanks, Andrew Robertson, Wellington
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